Wireless communication systems are widely used to provide voice and data communication between entities and customer equipment, such as between two mobile stations or units, or between a mobile station and a land line telephone user. As illustrated in FIG. 1, a typical communication system 10 as in the prior art includes one or more mobile units 12, one or more base stations 14 and a telephone switching office 16. In the provision of wireless services within a cellular network, individual geographic areas or “cells” are serviced by one or more of the base stations 14. A typical base station 14 as illustrated in FIG. 1 includes a base station control unit 18 and an antenna tower (not shown).
The control unit 18 comprises the base station electronics and is usually positioned within a ruggedized enclosure at, or near, the base of the tower. The control unit 18 is coupled to the switching office through land lines or, alternatively, the signals might be transmitted or backhauled through microwave backhaul antennas. A typical cellular network may comprise hundreds of base stations 14, thousands of mobile units or units 12 and one or more switching offices 16.
The switching office 16 is the central coordinating element of the overall cellular network. It typically includes a cellular processor, a cellular switch and also provides the interface to the public switched telephone network (PTSN). Through the cellular network, a duplex radio communication link may be established between users of the cellular network.
One or more passive antennas 20 are supported on the tower, such as at the tower top 22, and are oriented about the tower top 22 to provide the desired beam sectors for the cell. A base station will typically have three or more RF antennas and one or more backhaul antennas associated with each wireless service provider using the base station. The passive RF antennas 20 are coupled to the base station control unit 18 through multiple RF coaxial cables 24 that extend up the tower and provide transmission lines for the RF signals communicated between the passive RF antennas 20 and the control unit 18 during transmit (“down-link”) and receive (“up-link”) cycles.
The typical base station 14 as in the prior art of FIG. 1 requires amplification of the RF signals being transmitted by the RF antenna 20. For this purpose, it has been conventional to use a large linear power amplifier (not shown) within the control unit 18 at the base of the tower or other support structure. The linear power amplifier must be cascaded into high power circuits to achieve the desired linearity at the higher output power. Typically, for such high power systems or amplifiers, additional high power combiners must be used at the antennas 20 which add cost and complexity to the passive antenna design. The power losses experienced in the RF coaxial cables 24 and through the power splitting at the tower top 22 may necessitate increases in the power amplification to achieve the desired power output at the passive antennas 20, thereby reducing overall operating efficiency of the base station 14. It is not uncommon that almost half of the RF power delivered to the passive antennas 20 is lost through the cable and power splitting losses.
The RF cables 24 extending up the tower present structural concerns as well. The cables 24 add weight to the tower which much be supported, especially when they become ice covered, thereby requiring a tower structure of sufficient size and strength. Moreover, the RF cables 24 may present windloading problems to the tower structure, particularly in high winds.
Typical base stations also have antennas which are not particularly adaptable. That is, generally, the antennas will provide a beam having a predetermined beam width, azimuth and elevation. Of late, it has become more desirable from a standpoint of a wireless service provider to achieve adaptability with respect to the shape and direction of the beam from the base station.
Therefore, there is a need for a base station and antennas in a wireless communication system that are less susceptible to cable losses and power splitting losses between the control unit and the antennas.
There is also a need for a base station and associated antennas that operate efficiently while providing a linearized output during a transmit cycle.
It is further desirable to provide antennas which address such issues and which may be used for forming beams of a particular shape and direction.